Contact means



June 21, 1949. c. c. HEIN 2,473,884

CONTACT MEANS Filed lay 7, 1946 WITNESSES: INVENTOR (ar! C #6172.-

Patented June 21, 1949 CONTACT MEANS 7 Carl C. Hein, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation,

East Pittsburgh,

Pa... a corporation of Pennsylvania Application May 7, 1946, Serial No. 667,988

is so thin and fragile that some ancillary arrangement must be provided for obtaining good electrical contact from it to inleadlng wires.

In the past, one method has been to provide a spring washer of metal having a good electrical conductivity which makes contact over its central area with an insulating washer of substantial size bearing against the sprayed contact layer. This insulating washer sufilces to take up mechanical pressure which may be involved in mounting the separate rectifier units in seriallyrelated stacks or piles. The outer edges of the spring washer are bent downwardly to make a light but firm contact with the alloy layer and provide electrical conduction of the line current thereto.

Another type of contact has been used in which a metal washer of good conducting material bears directly on the surface of the sprayed metal. In such caset, the pressure necessary in assembling the separate units into stacks is suflicient to cause the sprayed metal, which is comparatively soft, to flow, and in course of time the change of dimensions resulting from this flow causes poor electrical contact. Furthermore, this pressure is transmitted to the electrical barrier layer at the surface of the selenium. It is impossible to spray the alloy with absolute uniformity of thickness and, as a result, high spots exist on the alloy. These high spots are subjected to the greatest pressure, as is likewise the portions of the barrier layer directly beneath them with the result that reverse leakage and electrical losses in the rectifier undergo an increase.

In accordance with my present invention, I improve upon the type of contact just mentioned by interposing between the metallic washer and the sprayed contact layer a material which serves to uniformly distribute the total pressure over the entire surface of the washer and thus eliminates the concentration of stress at points on the alloy as at present.

One object of my invention is, accordingly, to provide a method of making contact to the counter-electrode layer of dry rectiflers which shall be less subject to gradual change than were prior art arrangements for the same purpose.

Another object of my invention is to provide 3 Claims. (Cl. -366) a method of making contact to the counter electrode of a selenium rectifier in such a way as to uniformly distribute pressure over the contact surface.

Still another object of my invention is to provide a novel method for assembling a contact washer upon the surface of a sprayed metal counter-electrode on selenium rectifiers and the like.

Other objects of my invention will become apparent upon reading the following description, taken in connection with the drawing, in which the single figure is a cross-sectional view of a single unit selenium rectifier embodying the principles of my invention.

Referring in detail to the drawing, the selenium rectifier may comprise a nickel-plated iron base plate I having on one surface a layer 2 of metallic selenium. The other surface of the layer 2 is coated by metal spraying with a eutectic alloy of tin and cadmium or other suitable counterelectrode 3 now well known in the art. The methods of forming the unit so far discussed are too wellknown in the art to require detailed description here.

For convenience in mounting such rectiflers, they are frequently made in the form of discs or washers having a central hole 4 by which they may be supported on a through-bolt.

Since the layer 3 is generally too thin and delicate for attachment to inleading wires or other electrical connectors, I provide a metallic disc or washer 5 which covers the space immediately surrounding the hole 4.

. In accordance with the principles of my invention, I interpose between the counter-electrode 3 and the washer 5 some material 6 comprising a good electrical conductor which may be inserted as a relatively yielding layer between the counter-electrode 3 and the disc 5 and then hardened while in that position. For example, such a layer 6 may be interposed by coating the disc or the portion of the counter-electrode 3 adjacent thereto with silver-base lacquer. Such a material will harden in position and fill up the irregularities between the face of the counterelectrode 3 and the disc 5. Usually it will do this while still permitting the disc 5 to touch the peaks or higher points of the counter-electrode 3. Nevertheless, it will, when hardened, uniformly distribute over the surface subtended by the disc 5 any pressure applied to the outer surface of the washer.

Such an arrangement has the advantage over the spring-washer formation of contact described asvaees 3 above in that it is cheaper and easier to assemble and that it provides better thermal conductivity to carry away the heat generated in the rectifier itself. The application oi. protective varnishes is likewise facilitated.

I claim as my invention:

1. In combination with a dry-contact rectifier -for a counter-electrode which is relatively i'ragile, a contact washer separated from said counterelectrode by an intervening layer or silver-base lacquer.

2. The method of making contact to an electrode comprising a relatively fragile conductive layer which comprises providing a relatively inflexible contact plate and iilling the space between said plate and said electrode with a silverbase lacquer.

8. The method 01 making contact to an electrode comprising a relatively fragile conductive layer which comprises providing a relatively inflexible contact plate and lining the space between said plate and said electrode with a relatively yielding material which is capable oi being hardened in position after being put in place.

CARL cam.

REFERENCES CITED Thciollowingreieredcesareotrecordinthe tile or this patent:

UNITED STATE PATENTS Addink Aug. 7, 1945 

